Current computer systems, particularly smaller systems such as desk-top personal computers (PC's), portable and lap-top systems, are continuously being designed to reduce the sizes of the various electronic devices in such computers, while simultaneously increasing the number of pieces of information which can be processed by the computers. In the development of computers of smaller physical size, with ever increasing capacity, multiplex address/data buses, along with multiplex system controllers, have been developed; so that the address buses and data buses of the Central Processing Units (CPU's) share common buses for sequentially transferring groups of address and data information to the memory input/output devices and input/output only devices. The development of multiplex systems and the associated controllers has permitted a significant reduction in the number of required pins for the various I/O devices in the systems.
Even with the development of multiplex systems for personal, lap-top, or portable computers, significant price competition exists in the industry. Prices of electronic components of such computers are impacted by the number of separate integrated circuit components which are required and by the amount of valuable board space needed for those different components. Consequently, systems are periodically redesigned to place larger numbers of functions in integrated circuit packages having as few address and data pins on them as possible.
In the past, a separate read-only memory (ROM) has been required for the keyboard subsystem; and a physically separate ROM has been required for the operating system information (BIOS). The BIOS ROM used for the operating system is necessary at the initial boot of the system to effect the system boot. Once the computer system is functioning, following the initial boot, the keyboard subsystem ROM is used during the operation of the computer to provide the necessary keyboard operating information to the computer system. Although neither of these separate ROM devices usually are of large capacity, the fact that two physically separate ROM's are used causes an increase in the complexity of the system solution, particularly in view of the extra expense of separate packages and the mounting real estate required for these separate packages. Additional pins are required to interconnect the separate ROM's with other portions of the computer system, all of which provides an upward price pressure on the finished manufactured product. During the initial boot-up of the computer system, the keyboard subsystem ROM is not operated. In addition, following the initial boot-up of the system, the operating system (BIOS) ROM is not operated.
Accordingly, it is desirable to provide a computer system which has reduced cost and reduced complexity by combining the separate keyboard subsystem and operating system ROM's into a single larger ROM, thereby reducing the overall cost of the system through lowering of the number of parts required.